Squamous cell carcinoma of the head and neck (HNSCC) is the sixth most common type of cancer. Its incidence increased 60% recently in adults age 40 or less. Mortality among HNSCC patients is very high, often due to recurrence of primary disease. Major risk factors for HNSCC include tobacco and alcohol use. Data from this group and others suggest that estrogens may also contribute to the development of HNSCCs. The tobacco smoke carcinogen benzo(a)pyrene (B(a)P), ethanol from alcoholic drinks and the female hormone estrogen are all metabolized by cytochrome P450 (CYP) 1B1 to potentially carcinogenic metabolites. The hypothesis of the proposed studies is that a polymorphism in CYP1B1 (CYP1B1*2) confers a more aggressive disease phenotype and a greater risk of recurrence of HNSCC. Rationale for the role of CYP1B1 in HNSCC is provided by preliminary data that suggest that 1) the CYP1B1*2 polymorphism, which results in elevated basal expression of CYP1B1, confers increased risk of recurrence for HNSCC; 2) CYP1B1 protein is elevated in human HNSCCs as compared to non-neoplastic epithelium and 3) ethanol and estrogen induce CYP1B1 mRNA levels. In Aim 1, the effect of overexpressing a high-risk CYP1B1*2 allele vs wild type on selected biomarkers (cell proliferation, anchorage independence, invasion, survival, apoptosis and oxidative damage) will be evaluated in cultured premalignant oral leukoplakia (MSK-Leuki) cells following exposure to B(a)P, ethanol and estrogen. Results from studies in MSK-Leuki cells will be translated to an analysis of oral tissue from HNSCC patients in Aim 2. Patients with HNSCC will be genotyped for CYP1B1 (using TaqMan(R) assays) and the effect of the CYP1B1*2 allele on tumor recurrence will be examined in patients stratified by smoking, alcohol use and gender. Sections from tissue blocks from patients will be evaluated immunohistochemically for the level of biomarkers (apoptosis, proliferation and oxidative damage). The association of biomarker levels with CYP1B1 genotype will be investigated. The resulting data are anticipated to significantly enhance our understanding of the function of CYP1B1 in the recurrence of HNSCC and aid in determining the contribution of exposures to tobacco, estrogen and/or alcohol to recurrence in individuals carrying the high-risk CYP1Br2 allele.